58 



S ed. 



Testa, 

 Tegmen Aril. 



Albuminous 

 Ex albumin- 

 ous seeds. 



Cotyledons 

 Radicle and 

 Plumule of 

 Embryo. 



CHAPTER V. THE 'SEED AND FRUIT. 



54. The normal seed is en- 

 veloped in one or two outer coats which correspond to 

 the integuments of the ovule. The outer is usually firm 

 and often hard and is called the testa ; the inner, when it is 

 present, is thin and delicate and is called the tegmen. In some 

 cases there is an additional covering to the seed developed 

 after fertilisation has taken place and which is accordingly not 

 visible on the ovule. This covering usually originates from 

 the funicle or placenta but occasionally also from the micro - 

 pyle. It is known as an aril, e.g. the pulp of the Lichi. 



An outgrowth morphologically similar to an aril but 

 which is smaller and may develop from various parts of the 

 seed is called a caruncle, or sfrophiole. 



The testa of the seed sometimes grows out into a 

 membranous wing, as in Oroxylum indicum, see Fig. 1, Plate 

 XII, and sometimes is provided with long soft hairs, as in the 

 Cotton plant, these structures aiding the distribution of the 

 seed by wind. 



Inside the seed- coats we find what is popularly called the 

 kernel ; this may consist only of the embryo, or the latter may 

 occupy only a portion of it, the remainder of the kernel 

 consisting of the so-called albumen. (This is cellular tissue 

 densely packed with food-materials, such as starch, or other 

 substances, which are to serve as food for the young embryo.) 

 In the former case the seed is said to be exalbuminous and 

 in the latter albuminous. As examples of the former we may 

 take those of the Oak and Oroxylum indicum, see Figs. 1 and 2, 

 Plates I and XII, and of the latter the seed of the Pine (Pinus). 



If the albumen has originated inside the embrvo-sac it is 



o v 



called endosperm, if it is a part of the tissue of the nucellus it 

 is called perisperm. 



Albumen may be mealy (when it is easily broken into 

 powder), oily, fleshy, or hard, and even bony. If the outer 

 surface of the albumen is crumpled, or puckered, into narrow 

 folds it is said to be ruminate. 



In a well-developed embryo w r e can distinguish an axis 

 bearing one or more minute leaves ; these leaves are called 

 cotyledons. That part of the axis situated below the insertion 

 of the cotyledons and from which the primary root of the 

 seedling will be developed is called the radicle, while the part 

 of the axis above the cotyledons, which is the end of the 



